Conventionally, as an accessory drive system of this kind, one disclosed in Patent Literature 1 is known. This accessory drive system drives an accessory, such as a compressor for an air conditioner installed on a vehicle, using an internal combustion engine (hereinafter simply referred to as “the engine”) and an electric motor as drive sources, and is provided with the electric motor, first to third pulleys, and a clutch. The first pulley is provided on an output shaft of the above electric motor, the second pulley on a crankshaft of the engine, the third pulley on an input shaft of the accessory. Further, belts extend around the first to third pulleys, whereby the electric motor, the engine, and the accessory are connected to each other. A clutch is provided between the crankshaft and the second pulley, for connecting and disconnecting between the engine, the electric motor, and the accessory.
In the accessory drive system configured as above, during operation of the engine, the clutch connects the crankshaft and the accessory, whereby the accessory is driven by the engine. On the other hand, during stoppage of the engine, the clutch holds the crankshaft and the accessory in a disconnected state, and the accessory is driven by rotating the electric motor.
As described above, in the conventional accessory drive system, since the engine and the electric motor are used as drive sources of the accessory during operation and stoppage of the engine, the engine, the electric motor, and the accessory are connected to each other. Further, to prevent the friction of the engine from acting as load on the electric motor during stoppage of the engine, the clutch is provided for disconnecting between the engine, the electric motor, and the accessory only during stoppage of the engine, and is indispensable in the conventional accessory drive system. This brings about an increase in the size of the system, and an increase in the manufacturing costs. Further, when the engine is stopped or started during driving of the accessory, it is impossible to avoid generation of clutch noises, which results in degraded marketability thereof. Furthermore, since there is a limit to speed reduction by the pulley connecting between the engine and the accessory, the rotational speed of the input shaft of the accessory becomes high during high-speed operation of the engine, and to withstand the increased rotational speed of the input shaft, it is inevitable to increase the size of the accessory.
The present invention has been made to provide a solution to the above-described problems, and an object thereof is to provide an accessory drive system which is capable of achieving downsizing of the system, reduction of manufacturing costs thereof, and enhancement of marketability thereof.
[Patent Literature 1] Japanese Laid-Open Patent Publication (Kokai) No. 2000-179374.